The present invention relates to chair controls and, more specifically, chair controls which permit the chair back to be adjusted independently of the chair seat.
The present invention also relates to body weight chair controls in which the forces employed to adjust the chair back and chair seat are supplied by the user by shifting his or her weight within the chair.
In contrast, other common types of chair controls include a biased control attached only to the chair seat, such that the chair and back tilt at the same rate. An example of this type of construction is found in U.S. Pat. No. 3,386,770. This design has significant disadvantages partly due to the fact that the chair seat and chair back are maintained in fixed relationship regardless of the degree to which the chair is reclined. Furthermore, the configuration of the task, or fully forward, position of the chair cannot be varied. Consequently, the user may become fatigued as his body is maintained in one position while working for lengthy periods of time.
Other types of chair controls include synchrotilt chair controls in which the chair back and seat bolt tilt but at different rates to maintain a dynamic interrelationship between the seat and back. Examples of this type of chair control may be found in U.S. Pat. Nos. 2,796,918; 2,760,556; 2,615,496; and 2,612,211. Such chair controls also have significant drawbacks. First, although the inclination of the chair back relative to the chair seat is different for each reclined position of the chair, there is still only one chair back position for each seat position. Furthermore, neither the chair back nor the chair seat may be adjusted when the chair is in its task (i.e. fully forward) position.
Yet other prior art chair controls are attached only to the chair back, such that the back tilts but the seat does not. This type of control may be found for example in U.S. Pat. No. 2,272,980. This type of control also has serious drawbacks. First, the chair seat is not at all adjustable. Further, the position of the chair back cannot be varied when the chair is in its task position.
Body weight-actuated chair controls typically require complicated linkages for distributing the forces in the chair control so that no biasing means are required. The controls must be constructed so that the user's weight is somewhat evenly distributed throughout the chair, so that relatively slight shifts of body weight will result in movement or adjustment of the chair control.
One type of body weight chair control provides linkage between the back support and the seat support so that the seat is pushed forwardly and upwardly as the chair back is reclined. Examples of this type of control are shown in U.S. Pat. Nos. 2,796,918; 2,760,556; and 2,612,211. As with the earlier described dynamic chair controls, the angular relationship between the chair back and the chair seat cannot be varied, particularly when the chair is in its task position. Further, the angle of the chair seat in the task position cannot be adjusted.
Another type of body weight chair control pivots the chair seat and back precisely over the assembly's center of gravity. Consequently, a slight shift of weight by the user, not necessarily against the chair back, will result in movement of the chair control. An example of this type of control may be found in U.S. Pat. No. 2,615,496. This control is quite unstable because the center of gravity is so critically located and no biasing means are provided to alleviate the resultant instability of this location. Furthermore, there is only one chair back position for each angular orientation of the chair seat. Finally, the task position of this type of control may not be varied.
A further problem with all of the above-mentioned chair controls is that they are dynamic, rather than static, controls. Consequently, they do not generally lock and maintain one of the many possible configurations, a feature frequently desirable.